Date of Award

10-19-2015

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

Keywords

Aluminum, Finite element, Heat-affected zone, Identification, Residual stress

Supervisor

Ghrib, Faouzi

Rights

info:eu-repo/semantics/openAccess

Abstract

Welding is employed as a joining technique for aluminum in industries such as the automotive, construction, and aerospace. The heat generated by welding adversely affects the Heat-Affected Zone (HAZ) mechanical properties. Through numerical simulation techniques and experimental validation, a methodology was presented to analyze the gas metal arc welded aluminum components and predicted their mechanical behaviour. All major thermal, metallurgical, and mechanical phenomena were taken into account in the model development such as heat source, heat losses, as well as the effect of metallurgical phase transformations and temperature-dependent material properties. Simple methodologies were introduced to compute the hardening parameters of the HAZ in a welded 6061-T6 coupon specimen under uniaxial tensile loading using a digital image correlation technique. It was observed that the strength of the alloy decreased up to 35% in the weakest zone comparing to the base metal. Residual stress and distortion development in butt-joint were studied by the model validated with X-ray residual stress measurements. Between 65%-75% change in residual stresses was observed by different clamping condition during heating and cooling. The findings revealed that the tensile stress distributes along the weld line but reduces to compressive at the edges of the weld line. In addition, the hardness data of a welded L-joint from a previous study were adopted to validate the modelling methodology. It was concluded that for the alloy 6061-T6 with the thickness of 4.8 mm with low, medium, and high heat inputs, width of the HAZ are 8.9 mm, 15.1 mm, and 19.4 mm which are lower than the suggested value by the Canadian standard (25 mm). By comparing simulation results with and without the phase transformations, the error was observed between 9%-22% for hardness values on L- joints and between 19%-22% for the residual stress and about 23% and 20% difference in out-of-plane distortion in transverse and longitudinal directions of the butt-joint. At last, experimental and numerical efforts were carried out on strength capacity, and structural response of fillet welded alloy 6061-T6 plate-column joint under tensile testing that demonstrates a beam-column joint.

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